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How Much Wind Does a Wind Turbine Need?

There are more than 2,300 wind turbines spinning away and creating energy off the coasts of 11 European countries. A large number of those turbines are located in the North and Irish seas. One reason for that is because the winds blowing across those bodies of water are not only strong but also sustained.

It’s the same reason wind energy companies are eyeing the North Carolina coast as a possible location for wind farms. But that begs the question: just how much wind does a wind farm, or at least a wind turbine, need?

It shouldn’t surprise you to find out that, just as the wind constantly changes, wind turbines are built to operate within a wide range of wind specifications, so the answer varies.

Upwind turbines face into the wind, while downwind turbines face away. Some of the new generation of wind turbines can work at lower wind speeds, generally about five miles per hour. However these turbines are generally smaller, don’t generate as much energy, and are not designed to withstand higher wind ranges.

Most of what you would call large-scale wind turbines typically start turning in winds of seven to nine miles per hour. Their top speeds are around 50-55 mph, which is their upper safety limit. Large-scale wind turbines normally have a braking system that kicks in around 55 mph to prevent damage to the blades.

Ironically, many industrial-scale wind turbines require an electric 'kick-start' to begin turning. That’s what overcomes the inertia of getting the blades to start turning.

You might think that once the blades are turning, electricity is being generated.

But that’s not quite true, because the blades aren’t turning fast enough.

The blades are connected to a shaft that turns at between 30 to 60 rotations per minute. The shaft then connects to a gear box that increases the rotation speed from 1000 to 1800 rotations per minute, which is the speed required by most generators to produce electricity.

Of course, the amount of electricity a wind turbine generates depends on the size of the turbine, also known as the power rating, and how fast the wind is travelling at the turbine’s location. Wind turbines have a power rating usually ranging from 250 watts (enough to charge a battery) to 10 kilowatts (enough to power a house) to six megawatts (enough to power more than 1600 houses).

— Frank Graff

Frank Graff is a producer/reporter with UNC-TV, focusing on North Carolina Science Now, a weekly science series that airs Wednesdays, beginning in August 2013, as part of North Carolina Now on UNC-TV. In addition to producing these special segments, Frank will provide additional information related to his stories through this North Carolina Science Now Reporter's Blog!